1. Field of the Invention
The invention relates to a method and apparatus for ink jet printing, and, more particularly, to a method and apparatus for ink jet printing by a page wide ink jet printhead.
2. Description of the Related Art
Printers are one of the most popular computer peripherals. Not surprisingly, therefore, the rapid growth in acceptance, use, and numbers of computers during the past fifteen years has fueled the demand for, and interest in the development of, printers.
Presently employed printing techniques may generally be categorized as either impact printing or non-impact printing depending upon whether some portion of the printer "strikes" the print medium upon which characters are being printed. In an impact printer, some portion of the printer does strike the medium, e.g., paper. In a non-impact printer, on the other hand, only ink contacts the medium.
One of the most widely used types of non-impact printers at the present time is the so-called "ink jet printer." In ink jet printing, ink is ejected, most commonly by pressure, through a tiny nozzle to form an ink droplet that may be deposited on a paper medium. Ink jet printers have been developed that are capable of producing highly reproducible and controllable droplets. Using those printers, it is now possible for a droplet to be deposited at a location specified by digitally stored data.
Most commercially available ink jet printing systems may be generally classified as either "continuous jet" or "drop on demand" type. In a "continuous jet" type ink jet printing system, ink droplets are continuously ejected from a printer printhead and either directed to or away from a paper medium depending on the desired image to be produced. In such a continuous jet system, uniform ink droplets are formed from a stream of liquid continuously issuing from an orifice. A mechanism, often of an electromechanical material, such as piezoelectric material, oscillates in response to an applied voltage to cause break-up of the continuous stream into uniform droplets of ink and to impart an electrostatic charge to the droplets. High voltage deflection plates located in the vicinity of the ejected ink droplets selectively control the trajectory of the ink droplets causing the droplets to hit a desired spot on the paper medium. Since a continuous flow of ink is employed in this type system, it is referred to as continuous.
In a "drop on demand" type ink jet printing system, ink droplets are intermittently ejected from a printhead in response to a specific command related to the image to be produced. "Drop on demand" ink droplets are produced as a result of electromechanically induced pressure waves. The pressure waves are induced by applying a voltage pulse to an electromechanical material, e.g., a piezoelectric material, which is directly or indirectly coupled to a stored fluid. The pressure waves cause pressure/velocity transients to occur in the ink and these transients are directed so as to produce a droplet that issues from a reservoir or channel in the printhead, typically through an orifice. Since voltage is applied only when a droplet is desired, these types of ink jet printing systems are referred to as drop-on-demand.
As may be gathered from the discussion above, the use of piezoelectric materials in ink jet printers is well known. Most commonly, the piezoelectric materials are used in the form of a piezoelectric transducer by which electric energy is converted into mechanical energy. This conversion is caused by application of an electric field across the piezoelectric material, thereby causing the piezoelectric material to deform. This ability to distort piezoelectric material by application of an electric field has often been utilized in order to distort ink flow in continuous type systems and to force the ejection of ink in drop on demand type systems.
One drop on demand type ink jet printer configuration which utilizes the distortion of a piezoelectric material to eject ink includes a printhead forming an ink channel array in which the individual channels of the array each have side walls formed of a piezoelectric material. Typically, with respect to such arrays, the channels are micro-sized and are arranged so that the spacing between adjacent channels is relatively small. In operation of this type of printhead, ink is directed to and resides in the channels until selectively ejected therefrom. Ejection of ink from select channels is effected due to the electromechanical nature of the piezoelectric side walls of the channels. Because piezoelectric material deforms when an electric field is applied thereacross, the side walls of select channels may be caused to deform by applying an electric field thereacross. The electric field may be so selectively applied by digital or other means. This deformation of side walls of select channels reduces the volume of the respective channels creating a pressure pulse in the ink residing in those channels. The resultant pressure pulse then causes the ejection of a droplet of ink from the particular channel across which the electric field is applied.
In printing, the ink jet printhead in a typical ink jet printer is mechanically caused to move across the print medium, selectively ejecting ink from particular ink channels of the printhead in its movement thereacross, to print a particular line of print characters. Once the line is completed, the print medium mechanically progresses through the printer to position the printhead at the next line of the print medium. At the next line of the print medium the process is repeated with the printhead moving across the print medium to print the particular line of print characters, the print medium thereafter progressing to position the printhead at the next line. These steps of printhead movement across the print medium followed by progression of the print medium to position the printhead are repeated in the printing process until the entire print medium passes through the printer.
Printhead movement across the print medium in printing a line of characters is necessary in the typical ink jet printer arrangement because the printhead in such an arrangement has been generally narrow in width. Printhead width has generally been narrow due to a number of factors, including, among others, the integrated circuitry necessary to activate and drive the printhead, the minimal spacing required between ink ejection ports to create desired uniform print quality in each line of print characters, and the limited space available for printhead movement and operation in most printers. Such a typical printhead of narrow width restricts printing speed since two mechanical steps, printhead movement across print medium and print medium progression, are required. A trade-off design limitation to printing speed in the typical ink jet printer is print quality. Because the narrow printhead of the typical ink jet printer must be caused by digital or other means to selectively eject ink as the print medium is progressing through the printer and the printhead is simultaneously moving across the paper medium, print quality obtainable with such a printhead may be affected due to difficulties of timing ink ejection in coordination with print medium and printhead mechanical movement. There is, therefore, a trade-off between two limitations, printing speed and print quality, in the design of a narrow width printhead. It would be an improvement to overcome these limitations in ink jet printheads so that both printing speed and print quality could be increased in the same design without such trade-off limitations.
Attempts have been made to overcome these limitations by placing individual ones of the narrow printheads in a page wide alignment. In such an arrangement, individual ones of the narrow printheads are linked together to perform like a single-piece print bar. Ten to twenty individual printheads, instead of one united printhead, are required. Accuracy in alignment of the individual printhead nozzles in such an arrangement is critical to the quality of print from such a device, however, accuracy in alignment has heretofore been limited due to difficulties of linking the printheads to effect accurate alignment. Problems encountered in such an alignment of individual printheads include reduced print quality due to spacing requirements in aligning the printheads, a multiplicity of parts, for example, printheads and connector circuitry, leading to spacing limitations and increased malfunction risk, an involved manufacturing process comprising numerous steps with respect to each individual printhead and the integration thereof, and lack of positional accuracy due to limited means available to link the printheads and position printhead nozzles.
The present invention, being a page wide ink jet printhead comprising a single, united assembly integrating print nozzles, circuit connections and flip chip integrated circuits, and the method for manufacture thereof and printing thereby, overcomes these problems previously encountered.